The background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
Due to regulatory issues, it is currently necessary to prevent connection of cell phones in use on an aircraft to ground-based network rather than to on-board cellular base stations. Typically this is achieved by transmission of a noise signal by a dedicated system. Such systems are typically implemented using a network control unit (NCU), which includes a general control system that controls, configures, and monitors various noise generating units. Failure of such components can result in non-permitted connection of on-board cell phones to ground networks.
Typically, failure of the general control system is detected by expiration of a watchdog pulse. If the time span between two watchdog pulses arriving at a local network control unit exceeds a defined and configurable threshold, the network control unit will detect a system failure. Alternatively, the network control unit can detect the failure of the general controlling system by measuring the input power in a configurable frequency range, i.e. in particular the frequency range of the on-board cell. If the measured input power falls below a threshold, the network control unit detects a failure.
Generally the network control unit deactivates all noise generation units after expiration of the time between watchdog pulses, or when insufficient input power is registered. This can cause a problem if the passenger cell phones are still switched on. Since the noise generation in the network control unit is directly deactivated, the UEs might try to establish a connection to a ground network and since noise is not generated they will likely succeed.
Thus, there is still a need for improved network control systems and methods that are configured to inhibit passengers from connecting to a ground network.